Earnings Per Common Share - Computations of Basic Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income available to common shareholders:
Net income	$ 336,031	$ 286,688	$ 634,559	$ 528,301
Less: Preferred stock dividends	(20,317)	(20,317)	(40,635)	(40,635)
Net income available to common equity	315,714	266,371	593,924	487,666
Less: Income attributable to unvested stock-based compensation awards	(2,746)	(2,900)	(5,227)	(5,371)
Net income available to common shareholders	$ 312,968	$ 263,471	$ 588,697	$ 482,295
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	159,164	133,818	159,692	133,680
Less: Unvested stock-based compensation awards	(1,362)	(1,462)	(1,424)	(1,477)
Weighted-average shares outstanding	157,802	132,356	158,268	132,203
Basic earnings per common share	$ 1.98	$ 1.99	$ 3.72	$ 3.65